Wind Turbine Interactions with Wildlife and Their Habitats · WOODWARD MOUNTAIN WIND RANCH, PHOTO...

This summary reviews publicly available information about the adverse impacts of land-based wind power on wildlife in North America and the status of our knowledge regarding how to avoid or minimize these impacts.

BACKGROUND: SEMPRA RENEWABLES' AUWAHI WIND • INSET, L-R: EASTERN MEADOWLARK, PHOTO BY MATTHEW PAULSON, FLICKR • AMERICAN BALD EAGLE, PHOTO BY USFWS, FLICKR • HOARY BAT, PHOTO BY J. N. STUART, FLICKR

www.awwi.org • [email protected] • 202-656-3303

Wind Turbine Interactions

with Wildlife and Their Habitats

A Summary of Research Results

and Priority Questions

Last Updated with Latest Publicly Available Information: May 2019

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

INTRODUCTION

Wind energy’s ability to generate electricity without carbon emissions is expected to reduce the risk of potentially catastrophic effects to wildlife from unmitigated climate

change. Wind energy also provides several other environmental benefits including substantially reduced water withdrawals and consumption and decreased emissions of mercury and other sources of air and water pollution associated with the burning of fossil fuels (NRC 2010).

The siting and operation of wind energy facilities also pose a risk to some species of wildlife (Arnett et al. 2008; Strickland et al. 2011). Negative effects may include direct impacts in the form of individu-al fatalities resulting from collisions with turbine blades or towers, and indirect impacts resulting from the effects of the construction and operation of wind energy on a species’ use of habitat. For some species, concern exists that the cumulative effect of impacts from wind energy may contribute to population declines, especially as the installed capacity of wind energy increases.

To maximize wind energy’s benefits while addressing the risk to wildlife, a first step is to better understand the extent and nature of the risk. This summary seeks to do so by reviewing publicly available information about the adverse impacts of land-based wind power on

SMOKY HILLS WIND FARM, PHOTO BY DRENALINE, WIKIPEDIA

BLUE-WINGED TEAL, PHOTO BY ANDREA WESTMORELAND, FLICKR

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wildlife in North America and the status of our knowledge regard-ing how to avoid and minimize these impacts.

The amount of publicly available, peer-reviewed research con-tinues to grow, reflecting the ongoing interest in understanding wind-wildlife interactions. To maintain the highest level of scien-tific rigor for this summary, we have emphasized research that has been published in peer-reviewed journals or that appears in reports that have undergone expert, technical review.

This summary is updated and undergoes expert review on an an-nual basis. Literature citations supporting the information present-ed are denoted in parentheses; full citations can be found online at https://awwi.org/resources/summary-of-wind-power-interac-tions-with-wildlife/.

Organization of This Summary

Concerns about the adverse impacts of wind energy generation can be grouped broadly as direct or indirect impacts. We define direct

impacts to include fatalities resulting from collisions with turbine blades or towers. Indirect impacts result from the effects of the construction and operation of a wind energy facility on a species’ use of habitat. These impacts may include displacement of a species from suitable habitat and demographic effects due to fragmentation of habitat or disturbance from the construction and operation of a wind facility. This summary organizes statements about what is known and what remains uncertain regarding the adverse impacts of wind energy on wildlife in the following categories:

• Risk factors for collision fatalities

• Population-level consequences of collision fatalities

• Avoidance and minimization of collision fatalities

• Habitat-based impacts on birds

Within each section, statements are ordered in decreasing level of certainty. The level of certainty reflects the weight of evidence: we have more confidence in conclusions supported by multiple published studies than in conclusions based on only a single study. A single study, although informative, is usually insufficient for drawing broad conclusions.

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INTRODUCTION (CONTINUED)

Installed wind energy capacity in the United States continues to grow and was estimated at more than

96,000 megawatts (MW) at the end of 2018. The power ratings of turbines installed at new projects typically range from 1.5-3 MW, and turbine towers typically range in height from 80-100 m (260-325 feet). Turbine blades range in length from 38-60 m (125-200 feet) resulting in a maximum potential height of approximately 160 m (460 feet) and a rotor swept area of 0.45-1.13 hectares (1.1-2.8 acres). Blade tip speeds range from 220-290 km/hr (140-180 mph) under normal operating conditions. The perimeter of a wind facility may encompass thousands of acres. The most current wind market information can be found at the American Wind Energy Association’s website.

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RISK FACTORS FOR COLLISION FATALITIES

At many wind facilities, regular searches are conducted for birds and bats that collided with turbines. The number of studies reporting results of collision fatality monitoring at operating land-based wind energy facilities has increased substantially over the years, and studies conducted at more than 100 projects are publicly available (Arnett and Baerwald 2013; Loss et al. 2013a; Erickson et al. 2014; Thompson et al. 2017). Fatality reports for substantially more projects are stored within the American Wind Wild-life Information Center (AWWIC), a cooperative initiative of the American Wind Wildlife Institute (AWWI) and wind energy companies, which includes both public and private data (AWWI 2018, 2019). AWWIC also includes data from projects in regions that have few publicly available fatality reports, which should help address uncertainties about geo-graphic variation in collision fatalities of both birds and bats. In addition, protocols for carcass searches have become more standardized, and recent advances in estimating fatal-ities from raw carcass counts should facilitate comparisons of results from separate studies (Dalthorp et al. 2018).

This section outlines what is known and where there is remaining uncertainty about the patterns of bird and bat collision fatalities, particularly in the continental U.S. We first examine patterns that apply to both birds and bats, and then describe patterns specific to either birds or bats.

Birds and Bats

Fatalities of birds and bats have been recorded at all wind energy facilities for which records are publicly available.

We assume that most bird and bat collisions are with the ro-tating turbine blades, although collisions with turbine tow-ers are also possible. Fatality estimates of individual studies vary in how raw counts are adjusted for known sources of detection error and sampling intensity (Huso et al. 2016). Our understanding of these sources of error is improving, but comparisons or aggregations of fatality estimates, espe-cially if they include older studies (2006 or earlier), should be interpreted cautiously.

For birds, mean adjusted fatality rates from most studies range from 3 to 6 birds per MW per year1 for all species

combined (Strickland et al. 2011; Loss et al. 2013a; Erickson et al. 2014). In the larger data set contained with AWWIC, 75% of studies reported 3.1 or fewer fatalities per MW per year, with a median fatality estimate of 1.8 birds per MW per year (AWWI 2019; here, the median is reported instead of the mean because of the skewed distribution of fatality estimates).

Adjusted bat fatality rates tend to be higher and more vari-able than bird fatality rates, generally ranging from a mean

1 Fatality rates are typically reported on a per turbine basis or per name-plate capacity (MW). We report fatality rates per nameplate capacity to account for differences in turbine capacity, which range from 100 kw to 3.0 MW or more. We acknowledge that this reporting format has difficulties, especially when it comes to assessing the effects of repowering and the potential differences in fatalities due to variations in the physical compo-nents of the turbines.BLACK THROATED BLUE WARBLER, PHOTO BY KELLY COLGAN AZAR, FLICKR

LITTLE BROWN BATS, PHOTO BY USFWS, FLICKR

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of 4 to 7 bats per MW per year, but with some individual projects along forested ridgelines of the central Appala-chians reporting rates close to 50 bats per MW per year (Arnett et al. 2008; Strickland et al. 2011; Hein et al. 2013). Of the studies included in AWWIC, 75% reported estimates of fewer than five bat fatalities per MW per year, with a median of 2.7 bats per MW per year (AWWI 2018).

Bat fatality rates may vary substantially among regions in the U.S. while bird fatality rates do not

Adjusted fatality rates of bats are highest at facilities in the upper Midwest and eastern forests and tend be much lower throughout the Great Plains and western U.S. (Arnett and Baerwald 2013; Hein et al. 2013). Median adjusted fatal-ity estimates among studies contained in AWWIC ranged from 6.2 bats per MW per year in the Midwest to 0.7 bats per MW per year in the Pacific Northwest (AWWI 2018). A recent analysis suggested that the rate of bat fatalities was inversely related to the percent of grassland cover in prox-imity to wind facilities (Thompson et al. 2017), which might explain this pattern. However, other studies have failed to find similar relationships between bat fatality rates and land cover (Arnett et al. 2008, Arnett and Baerwald 2013). Re-gional variation in methodology for conducting fatality stud-ies may be an important confounding factor (AWWI 2018), and thus apparent differences in bat fatality rates among regions or habitats should be interpreted with caution.

There is relatively little geographic variation in the rate of bird fatalities per MW per year for all species combined (Erickson et al. 2014; AWWI 2019).

The lighting currently recommended by the Federal Aviation Administration (FAA) for installation on commercial wind turbines does not increase collision risk to bats and migrating songbirds.

The FAA regulates the lighting required on structures taller than 199 feet in height above ground level to ensure air traffic safety. The number of bat and songbird fatalities at turbines using FAA-approved lighting is not greater than that recorded at unlit turbines (Kerlinger et al. 2010; Bennett and Hale 2014). One study (Bennett and Hale 2014) recorded higher red bat fatalities at unlit turbines compared to those using red aviation lights; no differences were observed for other bat species between lit and unlit turbines. For wind turbines, the FAA currently recommends strobe or strobe-like lights that produce momentary flashes interspersed with dark periods up to three seconds in duration, and they allow commercial wind facilities to light a proportion of the turbines in a facility (e.g., one in five), firing all lights

synchronously (FAA 2007). Red strobe or strobe-like lights are frequently used.

The effect of turbine height and rotor swept area on bird and bat collision fatalities remains uncertain.

Some studies have suggested that bird and bat fatalities increase with tower height (Barclay et al. 2007; Baerwald and Barclay 2009; Loss et al. 2013). However, tower height was found not to affect levels of bat fatalities at Canadian facilities (Zimmerling and Francis 2016), and studies on birds suggest that the relationship between tower height and bird collisions is more nuanced (Smallwood and Karas 2009). Taller turbines often have much larger rotor-swept areas, and it has been hypothesized that collision fatalities will increase due to the greater overlap with flight heights of nocturnal-migrating songbirds and bats (Johnson et al. 2002; Barclay et al. 2007). The vast majority (>80%) of avian nocturnal migrants typically fly above the height of the most common rotor-swept zone (<500 feet; <150 m) (Mabee and Cooper 2004; Mabee et al. 2006), and there is no evidence to date that nocturnal migrants form a disproportionately high number of collision fatalities during migration (Welcker et al. 2017). In fact, nocturnal migrants tend to fly at greater heights than diurnal migrants, potentially reducing their risk of colliding with turbine blades (Aschwanden et al. 2018, Bruderer et al. 2018).

It is unknown whether collision risk at standalone

turbines is comparable to risk at individual turbines within large wind energy facilities.

Construction of single utility-scale turbines (1.5-2 MW) is growing rapidly in some regions of the country, especial-ly where opportunities for large utility-scale projects are limited or municipalities often supply their own electricity (e.g., Massachusetts). Fatality monitoring at single-turbine facilities is often not required, and published reports have not been available.

GRASSHOPPER SPARROW, PHOTO BY SHEILA GREGOIRE, FLICKR

DIRECT MORTALITY (CONTINUED)

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Birds

A substantial majority of bird fatalities at wind energy facilities are small passerines.

Studies contained within AWWIC reported 281 species of birds discovered during systematic searches for fatalities at wind energy facilities and an additional 13 more that were found incidentally (AWWI 2019). Raw counts of small passerines (<31 cm in length) account for approximately 57% of fatalities reported in both publicly available and private studies conducted at U.S. wind facilities (Erickson et al. 2014; AWWI 2019). Small passerines make up more than 90% of all landbirds (Partners in Flight Science Committee 2013). Searcher efficiency trials2 indicate that small birds have significantly lower detection rates than large birds (Peters et al. 2014), and the true proportion of passerine fatalities of all collision fatalities is uncertain. Modest peaks in fatality incidents of small passerines occur during spring and fall at most wind facilities, presumably reflecting the passage of migrants during these times (Strickland et al. 2011; Erickson et al. 2014; AWWI 2019).

2 Searcher efficiency trials involve placement of bird and bat carcasses to estimate the number of carcasses missed by field technicians during fatality surveys. This estimate is combined with other sources of detection error, such as scavenger removal of carcasses, to adjust the number of carcasses found during fatality surveys and provide a more accurate estimate of collision fatalities.

Fatalities of diurnal raptors are reported more often than expected given the relatively low abundance of these species.

Diurnal raptors account for approximately 8% of reported fatalities, which is more than expected given their pop-ulation size (AWWI 2019). This may reflect an increased vulnerability to collision among this group of birds or may be an artifact of the higher detectability of carcasses of large birds (Peters et al. 2014). Red-tailed hawk and American kestrel are the most commonly reported fatalities; they are also the two most abundant diurnal raptors in the U.S. and have carcasses that tend to persist longer than those of other species (DeVault et al. 2017; AWWI 2019). Golden eagle fatalities are uncommon and limited to the western U.S. (Pagel et al. 2013, AWWI 2019), but are of particular concern because of the small population size and slow life history (i.e., high adult survival and low reproductive rate) of the species.

Observed fatality incidents of prairie grouse are very low.

The vulnerability of prairie grouse to collide with turbines appears low; only greater sage-grouse and sharp-tailed grouse have been reported as fatalities, and numbers for both species were low (four and two carcasses, respectively) (AWWI 2019). Fatalities of some upland game birds, espe-cially the non-native ring-necked pheasant and gray par-tridge, are relatively common, accounting for approximately 4% of all bird fatalities (AWWI 2019).

Fatalities of waterbirds and waterfowl and other species characteristic of freshwater, shorelines, open water, and coastal areas (e.g., ducks, gulls and terns, shorebirds, loons and grebes) are reported infrequently at land-based wind

GOLDEN-CROWNED KINGLET, PHOTO BY ZANATEH, FLICKR

JUVENILE BALD EAGLE, PHOTO BY ELSIE.HUI, FLICKR

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facilities (Kingsley and Whittam 2007; Gue et al. 2013; AWWI 2019).

Repowering with newer, larger (≥ 1 MW) turbines may reduce raptor fatalities per MW at wind facilities compared to older, smaller (40 - 330kW) turbines.

The number of raptor fatalities on a per MW basis ap-pears to be declining substantially (67 – 96% depending on the species) at the Altamont Pass Wind Resource Area (APWRA) as a result of repowering: smaller, low-capacity turbines with varying types of support structures are being replaced with taller, higher-capacity turbines supported by mono-poles (Smallwood and Karas 2009; ICF Interna-tional 2016). Larger turbines complete fewer rotations per minute, which could possibly result in reduced raptor collision rates (NAS 2007). In addition, older turbines that use lattice support towers offer more perching sites for rap-tors, encouraging higher raptor occupancy in the immediate vicinity of the rotor swept area than large, modern turbines on tubular support towers (NAS 2007). Whether repowering leads to consistent reductions in fatalities will require addi-tional research at other facilities.

Bats

Migratory tree-roosting bat species are vulnerable to colliding with wind turbines.

At least 24 species of bats have been recorded as collision fatalities in North America, but a large majority of fatalities reported to date are from three migratory tree-roosting species (the hoary bat, the eastern red bat, and the sil-ver-haired bat), which collectively constitute approximately 70% of the reported fatalities at wind facilities for all North American regions combined (Kunz et al. 2007; Arnett et al. 2008; Arnett and Baerwald 2013; Hein et al. 2013; AWWI 2018).

Mexican free-tailed bats account for a significant percentage of bat fatalities in some parts of the U.S.

Mexican free-tailed bat, one of the most abundant bat spe-cies in the U.S. (Harvey et al. 2011), constitutes a substantial proportion (41–86%) of the estimated number of bats killed at facilities within this species’ range, which covers most of the southern half of the U.S. (Arnett et al. 2008; Miller 2008; Piorkowski and O’Connell 2010). It is unclear whether this species is at greater risk of collision than other bat species or if the frequency with which carcasses are discovered simply reflects its abundance.

Bat fatalities peak at wind facilities in the northern U.S. during the late summer and early fall migration.

Several studies in the northern U.S. have shown a peak in the incidence of bat fatalities in late summer and early fall, coinciding with the migration season of tree bats (Kunz et al. 2007; Arnett et al. 2008; Baerwald and Barclay 2011; Jain et al. 2011; Arnett and Baerwald 2013). A smaller peak in fatalities during spring migration has been observed for some bat species at some facilities (Arnett et al. 2008). In the larger sample of projects contained in AWWIC, the incidence of bat fatalities peaks in August in northern areas and September in areas further south, with no evidence of a spring peak (AWWI 2018).

Some bat species may be attracted to wind turbines.

It has been hypothesized that the relatively high number of bat fatalities that have been observed for some species and locations may be explained by attraction to wind turbines or wind facilities (Horn et al. 2008; Cryan and Barclay 2009). Several factors that might attract bats have been proposed, including the sounds produced by turbines, a concentration of insects near turbines, and bat mating behavior (Kunz et al. 2007; Cryan 2008; Cryan and Barclay 2009). Infrared imagery has shown bats exploring the nacelles of wind turbines from the leeward direction, especially at low wind speeds (Cryan et al. 2014). Insect surveys and analysis of the stomach contents of bat carcasses beneath turbines indi-cates a high degree of overlap between the items consumed by bats and the insects present around the turbine, suggest-ing that bats were foraging around the turbine blades at the time of death (Foo et al. 2017). The presence of deposits of bat feces on and around turbines further suggests that bats may feed near, and roost on, turbines (Bennett et al. 2017).

EASTERN RED BAT, PHOTO BY MATTHEW O’DONNELL, FLICKR

BIRDS (CONTINUED)

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However, hoary bats and silver-haired bats do not appear to concentrate their foraging activity in the vicinity of turbine blades, suggesting that while they may forage near tur-bines they are not necessarily attracted specifically to the rotor-swept zone (Reimer et al. 2018). Large percentages of male hoary, eastern red, and silver-haired bats carcasses found during periods of high fatality levels were at sexual readiness (Cryan et al. 2012).

Barotrauma does not appear to be an important source of bat mortality at wind energy facilities.

Forensic examination of bat carcasses found at wind energy facilities suggests that the importance of barotrauma, i.e., injury resulting from rapidly altered air pressure caused by fast-moving wind turbine blades (Baerwald et al. 2008), is substantially less than originally suggested (Rollins et al. 2012; Grodsky et al. 2011). The barotrauma hypothesis remains inadequately tested at this time.

Weather patterns may influence bat fatalities.

Bat activity is influenced by nightly wind speed and tempera-ture (Weller and Baldwin 2012), and some studies indicate that bat fatalities occur primarily on nights with low wind speed. Other weather-related variables such as temperature, wind direction, or changing barometric pressure may also be important (Baerwald and Barclay 2011). Migrating tree bats along a ridgeline in the Appalachian Mountains were more active at low wind speeds, high temperatures, and following significant drops in temperature (Mutherspaugh et al. 2019). Activity also varied across the course of a night, albeit in a species-specific fashion (Mutherspaugh et al. 2019). Addition-al research on weather patterns as a predictor of bat activity and fatalities could support mitigation efforts to reduce bat fatalities (Arnett et al. 2008; Baerwald and Barclay 2011; Weller and Baldwin 2012; Arnett and Baerwald 2013).

It is uncertain whether collision risk is higher for male

migratory tree bats than female migratory tree bats.

Examination of external characteristics of bat carcasses collected at wind energy facilities indicated that the sex ratio of migratory tree bats was skewed towards males (Arnett et al. 2008), although other studies show conflicting results (Baerwald and Barclay 2011). Bats can be a challenge to age and sex from external characteristics, especially when carcasses have decomposed or have been partially scavenged. The ability to accurately determine the sex of a bat carcass based on morphology declines significantly and rapidly as the carcass ages (Korstian et al. 2013; Nelson et al. 2018). Furthermore, the likelihood of misclassifying a female bat as a male bat increases as the carcasses ages (Nelson et al. 2018). Studies that have reported a male sex bias in fatalities used carcasses of varying ages and thus may be unreliable. Indeed, studies using molecular methods to sex bat carcasses show no evidence of a consistent sex bias in fatalities of tree bats (Korstian et al. 2013, Nelson et al. 2013), although male bias in fatalities may exist in other species such as evening bats (Korstian et al. 2013).

POPULATION-LEVEL

CONSEQUENCES OF COLLISION

FATALITIES

Reported levels of fatalities for some bird and bat species have raised concern for potential adverse impacts to popu-lations.

The estimated total number of collision fatalities of small passerine birds at wind energy facilities is likely several orders of magnitude lower than other leading anthropogenic sources of avian mortality.

Several recent estimates indicate that the number of small

passerine birds killed at wind energy facilities is a very small

HOARY BAT, PHOTO BY DANIEL NEAL, FLICKR

HORNED LARK, PHOTO BY KENNETH COLE SCHNEIDER, FLICKR

BATS (CONTINUED)

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fraction of the total annual anthropogenic bird mortality, and two to four orders of magnitude lower than mortality from other anthropogenic sources of mortality, including feral and domestic cats, power transmission lines, buildings and windows, and communication towers (Longcore et al. 2012; Calvert et al. 2013; Loss et al. 2014a,b,c; Loss et al. 2013a,b; Erickson et al. 2014). Collision fatalities from wind turbines may be relatively more important among the sourc-es of anthropogenic mortality that affect diurnal raptors, including golden eagles (USFWS 2016).

Fatality rates at currently estimated values do not appear likely to lead to population declines in most bird species.

For small passerine species, current turbine-related fatalities constitute a very small percentage of their total population size (typically <0.02%), even for those species with the most frequently reported fatality incidents (Kingsley and Whittam 2007; Kuvlesky et al. 2007; Erickson et al. 2014). However, detailed demographic modeling indicates a potential for population-level impacts at current or projected levels of collision fatalities for some raptor species (Carrete et al. 2010; Bellebaum et al. 2013; Hunt et al. 2017).

The status of bat populations is poorly understood, and the ecological impact of bat fatality levels is not known.

Bats are long-lived, and many species have relatively low reproductive rates, making populations susceptible to local-ized extinction (Barclay and Harder 2003; Jones et al. 2003). Population sizes for migratory tree bat species are unknown, and we don’t know whether current or future collision fatality levels represent a significant threat to these spe-cies (Kunz et al. 2007; Arnett et al. 2008; Arnett and Baer-wald 2013). Studies have focused on estimating effective population sizes of tree bats from genetic data, and these estimates might be useful as baselines for evaluating future impacts of collision mortality and other threats to bats (Korstian et al. 2015; Vonhof and Russell 2015; Sovic et al. 2016). Detailed demographic modeling indicates a potential for population-level impacts at current or projected levels of collision fatalities for hoary bats (Frick et al. 2017).

The ecological implications of White-Nose Syndrome and collision fatalities for bats are not well understood.

White-Nose Syndrome (WNS) is a fungus-caused disease that is estimated to have killed millions of bats in North America since it was first discovered (Frick et al. 2010;

Turner et al. 2011; Hayes 2012). Cave-dwelling bats are most at risk, and it is unknown whether WNS will be a significant source of mortality in migratory tree bats, which have been identified in the U.S. as being particularly vulnerable to collisions at the majority of the wind facilities at which they occur. Migratory tree bats rarely occur in caves, and their solitary nature may not facilitate the spread of fungal spores (Foley et al. 2011). Because cave-dwelling bats represent a higher percentage of fatalities at Midwestern wind energy facilities, there is concern about the added mortality of wind turbine collisions to WNS-vulnerable bat species in this re-gion, some of which may have declined in numbers by more than 90% (Frick et al. 2010).

AVOIDANCE AND

MINIMIZATION OF

COLLISION FATALITIES

Siting

Substantial effort is made to estimate collision risk of birds and bats prior to the siting, construction, and operation of wind energy facilities under the premise that high-activity sites will pose an unacceptable risk to these species and should be avoided. Many wind energy companies choose to apply a tiered decision-making process as outlined in the Land-based Wind Energy Guidelines issued by the U. S. Fish

DILLON WIND POWER PROJECT, PHOTO BY IBERDROLA RENEWABLES, INC., NREL 16105

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and Wildlife Service in 2012. This approach, developed with input from multiple stakeholders, outlines a series of steps companies can take to identify potential threats to species thought to be at risk from wind energy development.

Siting individual turbines away from topographic features that attract concentrations of large raptors may reduce raptor collision fatalities at wind energy facilities.

Some analyses have indicated a relationship between raptor fatalities and raptor abundance (Strickland et al. 2011; Carrete et al. 2012; Dahl et al. 2012), although studies also suggest that raptor activity as measured by standard activity surveys may not correlate with the number of raptor fatalities resulting from collisions with turbines (Ferrer et al. 2012). Large raptors are known to take advantage of wind currents created by ridge tops, upwind sides of slopes, and canyons that are favorable for local and migratory move-ments (Bednarz et al. 1990; Barrios and Rodriguez 2004; Hoover and Morrison 2005; de Lucas et al. 2012; Katzner et al. 2012; Poessel et al. 2018; Marques et al. 2019).

The relationship between bird behavior and bird collision risk, especially near the rotor swept area, is

complex and not well understood.

The foraging behavior of some species, such as red-tailed hawk, may take them into close proximity to the rotor-swept zone and possibly explain relatively high fatality rates. Other species, such as common raven, fly around wind turbines and appear to actively avoid collisions with turbines (King-sley and Whittam 2007; Kuvlesky et al. 2007). High prey density (e.g., small mammals) is presumed to be a principal factor responsible for high raptor use and collision rates at the Altamont Pass Wind Resource Area (Kingsley and Whit-tam 2007; Kuvlesky et al. 2007; NAS 2007; Smallwood and Thelander 2008). Bayesian models of raptor collision risk have been developed to predict fatalities based on observed raptor activity in the area and estimated collision probability (New et al. 2015).

The ability to predict collision risk for birds and bats from activity recorded by radar and acoustic detectors, respectively, remains elusive.

The use of radar and bat acoustic detectors is a common feature of pre-construction risk assessments for siting wind energy facilities (Strickland et al. 2011). To date, stud-ies have not been able to develop a quantitative model enabling reasonably accurate prediction of collision risk to birds and bats from these surveys (Hein et al. 2013). Predicting bat collision risk using pre-construction activity

measures would be further complicated if bats are attracted to wind turbines (see above).

Variation in bat fatality rates may be influenced by land-scape features affecting activity and migration routes.

Activity of migratory bats may be influenced by landscape features such as valleys, ridgelines, and riparian systems, and the variation in activity among these features may be related to the geographical variation in fatality rates (Baer-wald and Barclay 2009; Santos et al. 2013). Relating fatality rates to landscape features around a wind energy facility could be useful in siting wind farms to avoid higher-risk ar-eas (Kunz et al. 2007; Kuvlesky et al. 2007; NAS 2007; Arnett et al. 2008; Santos et al. 2013).

Operations

Wind energy companies are also employing a variety of technologies and operational techniques to minimize fatali-ties of vulnerable species at operating wind energy facilities.

Curtailing blade rotation at low wind speeds results in substantial reductions bat fatalities.

An examination of ten separate studies (Baerwald et al. 2009; Arnett et al. 2011; Arnett et al. 2013b) showed reductions in bat fatalities ranging from 50 to 87% when compared to normally operating turbines. Further study to identify times when bat collision risk is high could optimize

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timing of curtailment and minimize power loss (Weller and Baldwin 2012; Martin et al. 2017; EPRI 2017). For example, a smart curtailment approach that combined real-time data on wind speed and bat activity near turbines reduced esti-mated fatalities of all bats at a facility by nearly 85% while reducing the overall curtailment time by nearly 50% (Hayes et al. 2019). Power generation at treatment turbines was reduced by 3% relative to turbines that were not curtailed (Hayes et al. 2019).

Selective shutdown of high-fatality turbines may be an effective strategy for reducing fatalities of some raptor species.

Some of the highest raptor fatality rates have been ob-served in southern Spain where raptors congregate to cross the Strait of Gibraltar to Africa during migration (Ferrer et al. 2012). One study (de Lucas et al. 2012) reported a substan-tial reduction of griffon vulture fatalities (mean of 50.8%) at a facility due to selective shutdown of turbines where the greatest number of fatalities was observed.

Automated monitoring may allow for smart

curtailment strategies that reduce fatalities of raptors and other large birds.

Automated systems can successfully detect and classify ea-gles in the vicinity of a wind project, and are able to detect large birds at far greater distances than human observers (McClure et al. 2018). Ongoing research will test the ability of camera-based systems to track eagles in flight, determine when they are at risk of colliding with a turbine, and issue successful curtailment orders.

The use of an automated detection and acoustic deterrent may reduce the risk of raptor fatalities.

An integrated detection and deterrent system was shown to detect and track large birds approaching wind turbines and trigger auditory warning signals that appeared to deter raptors from approaching wind turbines and reduce collision risk (H.T. Harvey & Associates 2018). Improvements in detec-tion would reduce false positives that result in unnecessary triggering of the auditory deterrents. Ongoing research will further evaluate the ability of such systems to reduce raptor fatality rates.

The use of ultrasonic transmitters may deter bats away from rotor swept areas and reduce bat fatalities.

Experimental trials have shown that ultrasonic devices can reduce bat activity and foraging success, and evaluation of similar devices installed on wind turbines has shown some

reduction in bat fatalities over control turbines (Arnett et al. 2013a). Development of bat deterrents using both acoustic and visual stimuli remains an active area of research (EERE 2015).

Efforts intended to increase turbine visibility and reduce collision fatalities have met with limited success.

Impact minimization methods that are assumed to make turbine blades more visible to birds have been proposed to reduce collisions with wind turbines. For example, it has been hypothesized that towers and blades coated with ultraviolet (UV) paint may be more visible to birds, making them easier to avoid. In the only known test, Young et al. (2003) compared fatality rates at turbines with UV coatings to turbines coated with standard paint and found no differ-ence. Several raptor species have shown little response to ultraviolet light (Hunt et al. 2015). Few data are otherwise available on the effectiveness of these and other potential methods for making turbines more visible to birds.

WHOOPING CRANES, PHOTO BY GILLIANCHICAGO, FLICKR

AVOIDANCE AND MINIMIZATION OF COLLISION FATALITIES (CONTINUED)

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HABITAT-BASED IMPACTS

ON BIRDS

Species’ use of habitat can be affected by the construction and operation of a wind energy facility. Impacts can include disturbance, displacement from suitable habitat, or demo-graphic effects due to fragmentation of habitat or changes in prey resources. The section below outlines what is known and where there is remaining uncertainty about habi-tat-based impacts on birds.

Operating wind energy facilities can reduce abundance of some bird species, but the effect is not consistently observed in all studies.

Studies have indicated displacement of bird species in response to wind energy development, with some species showing consistent decreases in abundance in proximity to turbines, while other species showed no effect (Hatchett et al. 2013; Loesch et al. 2013; Stevens et al. 2013; Shaffer and Buhl 2016; Fernández-Bellon et al. 2019).

It has been suggested that high site fidelity in some grass-land bird species may reduce displacement effects in the short-term, but that displacement would become more pro-nounced over time. However, this effect was not apparent in a 10-year study of grassland birds (Shaffer and Buhl 2016). It is also unknown whether bird species will habituate to wind energy facilities and whether disturbance effects diminish over time (see Shaffer and Buhl 2016). In a UK study, three species declined in abundance during construction of wind energy facilities; the effect persisted for two of the species, both shorebirds, but red grouse density returned to pre-construction levels after the facility became operational (Pearce-Higgins et al. 2012).

There is concern that prairie chickens and greater

sage-grouse will avoid wind energy facilities because of disturbance or because they perceive turbine towers as perches for avian predators.

Research indicates that close proximity to roads, utility poles or lines, trees, oil and gas platforms, and/or human habitations causes displacement in prairie chickens and

sage-grouse (Robel et al. 2004; Kingsley and Whittam 2007; Kuvlesky et al. 2007). It is hypothesized that similar effects would result from wind energy development, but few published studies have tested this hypothesis (Walters et al. 2014).

An extensive and comprehensive multi-year study of greater prairie-chickens in a fragmented Kansas landscape showed neutral, positive, and negative responses to wind energy development as measured by a variety of demographic pa-rameters. There was little or no response in nesting females (Winder et al. 2013; Winder et al. 2014); lek persistence appeared to be lower in proximity to turbines, but there was no detectable effect of turbine proximity on male body mass (Winder et al. 2015).

A multi-year study of greater sage-grouse in Wyoming found that many demographic and habitat use factors, including selection of nest sites and nest, brood, and female survival were not influenced by proximity to turbines (LeBeau et al. 2017a). However, selection of brood rearing and post-rear-ing habitat was negatively influenced by ground disturbance related to roads and turbine pads (LeBeau et al. 2017a). Negative trends in male lek attendance were not detected (LeBeau et al. 2017b).

It is unknown whether wind energy facilities decrease habitat quality or act as barriers to landscape-level movements by big game and other large terrestrial vertebrates.

There are a small number of studies that have evaluated the hypothesis that land-based wind energy facilities negatively affect non-flying wildlife. Proximity to a wind energy facility did not affect winter survival of pronghorn in Wyoming (Taylor et al. 2016). Development and operation of a wind energy facility in Oklahoma had no measurable impact on radio-collared Rocky Mountain elk (Walter et al. 2006). Long-term studies of desert tortoise at a California wind en-ergy facility have found no negative effects on tortoises us-ing the area encompassed by the facility (Lovich et al. 2011; Ennen et al. 2012); survival of tortoises was higher within the area of the facility than in an adjacent undisturbed area (Agha et al. 2015).

About AWWIThe American Wind Wildlife Institute is a partnership of leaders in the wind industry, wildlife management agencies, and science and environmental organizations who collaborate on a shared mission: to facilitate timely and responsible development of wind energy while protecting wildlife and wildlife habitat.

www.awwi.org • [email protected] • 202-656-3303

Suggested Citation: American Wind Wildlife Institute (AWWI). 2019. Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions. Washington, DC. Available at www.awwi.org.

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